Graphite-containing refractory and method of producing graphite-containing refractory

ABSTRACT

A graphite-containing refractory has higher bending strength and fracture energy than known refractories. The graphite-containing refractory has a graphite content of 1% to 80% by mass. 1000 to 300000 carbon fibers with a fiber diameter of 1 to 45 μm/fiber are bundled. The carbon fiber bundle has a length of 100 mm or more and is placed within the graphite-containing refractory to form the same.

TECHNICAL FIELD

This disclosure relates to a graphite-containing refractory within whicha carbon fiber bundle is placed and a method of producing thegraphite-containing refractory.

BACKGROUND

Equipment (refining vessels, transfer vessels and the like) used in aniron making process or a steelmaking process in steelworks has arefractory lining to withstand its use under high temperatures forextended periods. Magnesia carbon refractories are used in converters ina refining process. Torpedoes and hot metal ladles used in a hot metalpretreatment process are lined with an alumina-silicon carbide-carbonrefractory. These refractories are used under very severe conditions,including mechanical impacts during charging, abrasion by agitation ofmolten steel and molten slag, slag erosion by molten slag, and suddentemperature changes in operation. Thus, using durable refractories thatcan withstand severe conditions are desirable for stable operation.

Japanese Unexamined Patent Application Publication No. 2005-320196discloses, as a technique to improve durability of a refractory, arefractory within which a rod-like or net-like high-strength fiberbundle is stiffened with a synthetic resin or the like and is placedwithout deformation of the high-strength fiber bundle. It states thatplacing the high-strength fiber bundle within the refractory withoutdeformation can improve the mechanical strength and spalling resistanceof the refractory. Japanese Unexamined Patent Application PublicationNo. 2007-106618 discloses a refractory in which a unidirectional bundle,twine, or fabric made of high tensile fibers is bonded to part or all ofthe surface of the refractory with a heat-resistant adhesive. It statesthat such a unidirectional bundle, twine, or fabric made of high tensilefibers bonded to part or all of the surface of the refractory canimprove the tensile strength, reduce the occurrence of cracks orfracture, and thereby prolong the life of the refractory.

Carbon fibers placed in the refractories disclosed in JapaneseUnexamined Patent Application Publication No. 2005-320196 and JapaneseUnexamined Patent Application Publication No. 2007-106618 have a lengthof 90 mm or less, and the refractories have insufficient strength asrefractories for use in converters or the like exposed to severeconditions. It could therefore be helpful to provide agraphite-containing refractory having higher bending strength andrequiring higher energy to be destroyed (hereinafter referred to as“fracture energy”) than known refractories and a method of producing thegraphite-containing refractory.

SUMMARY

We thus provide:

-   (1) A graphite-containing refractory with a graphite content of 1%    to 80% by mass, containing a carbon fiber bundle 100 mm or more in    length placed therein, the carbon fiber bundle being formed of 1000    to 300000 carbon fibers with a fiber diameter of 1 to 45 μm/fiber.-   (2) The graphite-containing refractory according to (1), wherein the    carbon fiber bundle is formed of 1000 to 60000 of the carbon fibers.-   (3) The graphite-containing refractory according to (1) or (2),    containing a magnesia raw material constituting 20% to 99% by mass    of the graphite-containing refractory.-   (4) The graphite-containing refractory according to (1) or (2),    containing an alumina raw material constituting 10% to 95% by mass    of the graphite-containing refractory and a silicon carbide raw    material constituting 1% or more by mass of the graphite-containing    refractory.-   (5) The graphite-containing refractory according to (4), further    containing a silica raw material constituting 1% to 50% by mass of    the graphite-containing refractory.-   (6) The graphite-containing refractory according to (1) or (2),    containing a refractory waste constituting 10% to 90% by mass of the    graphite-containing refractory, the refractory waste being a crushed    used refractory.-   (7) The graphite-containing refractory according to any one of (1)    to (6), wherein the carbon fiber bundle is formed by bonding using    at least one adhesive selected from a phenolic resin, an alumina    sol, a silica sol, pitch, and tar.-   (8) The graphite-containing refractory according to any one of (1)    to (6), wherein the carbon fiber bundle is formed by bonding using    at least one adhesive selected from a phenolic resin, an epoxy    resin, a melamine resin, a urea resin, an alkyd resin, an    unsaturated polyester resin, polyurethane, thermosetting polyimide,    an alumina sol, a silica sol, a zirconia sol, a chromia sol, a    titania sol, a magnesia sol, a calcia sol, an yttria sol, pitch,    tar, and a starch paste.-   (9) The graphite-containing refractory according to any one of (1)    to (8), further containing short carbon fibers constituting 0.10% to    10% by mass based on 100% by mass of the graphite-containing    refractory, the short carbon fibers having a fiber diameter of 1 to    45 μm/fiber, a fiber length of 1 mm or less, and a ratio of fiber    length to fiber diameter (fiber length/fiber diameter) of 2 to 1000.-   (10) A method of producing a graphite-containing refractory within    which a carbon fiber bundle is placed, the graphite constituting 1%    to 80% by mass, the method including: a bundling step of bundling    carbon fibers to form the carbon fiber bundle; a mixing step of    mixing a refractory raw material with graphite to prepare a    graphite-containing refractory raw material; a pressing step of    pressing the graphite-containing refractory raw material in which    the carbon fiber bundle is placed to prepare a pressed product; and    a drying step of drying the pressed product, wherein the bundling    step includes bundling 1000 to 300000 of the carbon fibers with a    fiber diameter of 1 to 45 μm/fiber to form a carbon fiber bundle 100    mm or more in length.-   (11) The method of producing a graphite-containing refractory    according to (10), wherein the bundling step includes bundling 1000    to 60000 of the carbon fibers.-   (12) The method of producing a graphite-containing refractory    according to (10) or (11), wherein the refractory raw material is a    magnesia raw material, and the mixing step includes adding 20% to    99% by mass of the magnesia raw material.-   (13) The method of producing a graphite-containing refractory    according to (10) or (11), wherein the refractory raw material    includes an alumina raw material and a silicon carbide raw material,    and the mixing step includes adding 10% to 95% by mass of the    alumina raw material and adding the silicon carbide raw material at    1% or more by mass.-   (14) The method of producing a graphite-containing refractory    according to (13), wherein the refractory raw material includes an    alumina raw material, a silicon carbide raw material, and a silica    raw material, the mixing step includes adding 10% to 95% by mass of    the alumina raw material, adding the silicon carbide raw material at    1% or more by mass, and adding 1% to 50% by mass of the silica raw    material.-   (15) The method of producing a graphite-containing refractory    according to (10) or (11), wherein the refractory raw material is a    refractory waste, which is a crushed used refractory, and the mixing    step includes adding 10% to 90% by mass of the refractory waste.-   (16) The method of producing a graphite-containing refractory    according to any one of (10) to (15), wherein the bundling step    includes bonding the carbon fibers with at least one adhesive    selected from a phenolic resin, an alumina sol, a silica sol, pitch,    and tar.-   (17) The method of producing a graphite-containing refractory    according to any one of (10) to (15), wherein the bundling step    includes bonding the carbon fibers with at least one adhesive    selected from a phenolic resin, an epoxy resin, a melamine resin, a    urea resin, an alkyd resin, an unsaturated polyester resin,    polyurethane, thermosetting polyimide, an alumina sol, a silica sol,    a zirconia sol, a chromia sol, a titania sol, a magnesia sol, a    calcia sol, an yttria sol, pitch, tar, and a starch paste.-   (18) The method of producing a graphite-containing refractory    according to any one of (10) to (17), further including, before the    pressing step: a kneading step of kneading the graphite-containing    refractory raw material; and a filling step of filling a mold to    press the graphite-containing refractory raw material with the    kneaded graphite-containing refractory raw material and the carbon    fiber bundle.-   (19) The method of producing a graphite-containing refractory    according to (18), wherein the filling step includes filling 5% or    more by volume of the mold with the graphite-containing refractory    raw material, then placing the carbon fiber bundle at intervals of 3    mm or more, and repeatedly performing the filling and the placing to    fill the mold with the graphite-containing refractory raw material    and the carbon fiber bundle.-   (20) The method of producing a graphite-containing refractory    according to any one of (10) to (17), further including, before the    pressing step: a kneading step of kneading the graphite-containing    refractory raw material; and a filling step of filling a pressing    vessel to press the graphite-containing refractory raw material with    the kneaded graphite-containing refractory raw material and the    carbon fiber bundle, wherein the pressing step includes applying    pressure to the pressing vessel via a pressure medium to prepare a    pressed product.-   (21) The method of producing a graphite-containing refractory    according to any one of (10) to (20), wherein the mixing step    includes adding short carbon fibers constituting 0.10% to 10% by    mass based on 100% by mass of the graphite-containing refractory raw    material, the short carbon fibers having a fiber diameter of 1 to 45    μm, a fiber length of 1 mm or less, and a ratio of fiber length to    fiber diameter (fiber length/fiber diameter) of 2 to 1000.

A graphite-containing refractory with higher bending strength andfracture energy than before can be produced by placing a carbon fiberbundle 100 mm or more in length within the graphite-containingrefractory. The use of such a graphite-containing refractory with higherbending strength and fracture energy, for example, as a converterrefractory enables stable converter operation and can prolong the lifeof the graphite-containing refractory.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) include a perspective view and a side view of amagnesia carbon refractory according to an example.

FIG. 2 is a perspective view of a carbon fiber bundle.

FIG. 3 is a schematic perspective view of the magnesia carbon refractoryused as a converter refractory.

FIGS. 4(a) and 4(b) include a perspective view and a side view of themagnesia carbon refractory in which the angle θ2 between the directionperpendicular to the pressing surface of the magnesia carbon refractoryand the direction along the length L1 of the carbon fiber bundle is 45degrees.

FIGS. 5(a) and 5(b) include a perspective view and a side view of themagnesia carbon refractory in which the angle θ2 between the directionperpendicular to the pressing surface of the magnesia carbon refractoryand the direction along the length L1 of the carbon fiber bundle is 135degrees.

FIG. 6 is a production flow diagram of the magnesia carbon refractoryaccording to an example.

FIGS. 7(a) and 7(b) include explanatory views of a CIP pressing method.

FIGS. 8(a) and 8(b) include schematic cross-sectional views of anerosion test in a high-frequency induction furnace.

FIG. 9 is a load-displacement curve obtained by a three-point bendingtest method.

FIGS. 10(a)-10(c) include schematic cross-sectional views illustratingthe charge angles of carbon fiber bundles in Examples 9-1 to 9-3.

FIG. 11 is a schematic cross-sectional view of the state of pressing bya CIP apparatus.

FIGS. 12(a)-12(c) include schematic cross-sectional views illustratingthe charge angles of carbon fiber bundles in Examples 10-1 to 10-3.

FIG. 13 is a schematic cross-sectional view of the state of pressing bya CIP apparatus.

REFERENCE SIGNS LIST

10 magnesia carbon refractory

12 magnesia carbon raw material

14 carbon fiber bundle

16 pressing surface

18 dotted line

20 arrow

30 supporting member

32 core metal

34 upper supporting plate

35 lower supporting plate

36 pressing vessel

38 CIP apparatus

40 pressure medium

50 high-frequency induction furnace

52 induction coil

54 bottom plate

56 molten iron

58 synthetic slag

60 graphite-containing refractory

DETAILED DESCRIPTION

Magnesia carbon refractories used to line converters are used under verysevere conditions, including mechanical impacts during charging,abrasion by agitation of molten steel and molten slag, slag erosion bymolten slag, and sudden temperature changes in the operation of theconverters. Thus, it is required to use magnesia carbon refractoriesthat can withstand such severe conditions for stable operation.Likewise, alumina-silicon carbide-carbon refractories used to linemolten iron preliminary treatment vessels such as torpedoes or hot metalladles, are also used under very severe conditions. Thus, durablealumina-silicon carbide-carbon refractories that can withstand theseconditions are preferably used.

We found that placing a carbon fiber bundle 100 mm or more in lengthcomposed of 1000 to 300000 carbon fibers with a fiber diameter of 1 to45 μm/fiber within a graphite-containing refractory can improve thebending strength and fracture energy of the refractory compared to knowngraphite-containing refractories. Our methods are further describedbelow with an example of a magnesia carbon refractory.

FIGS. 1(a) and 1(b) include a perspective view and a side view of amagnesia carbon refractory 10 according to an example. FIG. 1(a) is aperspective view of the magnesia carbon refractory 10, and FIG. 1(b) isa side view of the magnesia carbon refractory 10. The magnesia carbonrefractory 10 includes a plurality of carbon fiber bundles 14 placed inthe longitudinal direction within a magnesia carbon raw material 12,which is a mixture of graphite and a magnesia raw material. Thisincreases the bending strength and fracture energy of the magnesiacarbon refractory 10.

The graphite constitutes 1% to 80% by mass of the magnesia carbonrefractory 10, and the magnesia raw material constitutes 20% to 99% bymass of the magnesia carbon refractory 10. This can prevent cracking ofthe refractory caused by thermal spalling and improve resistance toerosion by converter slag. By contrast, a graphite content of less than1% by mass results in cracking of the refractory caused by thermalspalling and results in significantly decreased crack resistance. Amagnesia raw material content of less than 20% by mass results indecreased resistance to erosion by converter slag and results inincreased erosion.

FIG. 2 is a perspective view of one of the carbon fiber bundles 14. Thecarbon fiber bundle 14 is formed by bundling a plurality of carbonfibers. The carbon fiber bundle 14 has a length L1 of 100 mm or more,which is smaller than or equal to the length of the magnesia carbonrefractory 10 in the longitudinal direction of the carbon fiber bundles14 placed within the magnesia carbon refractory 10. The carbon fiberbundle 14 is composed of 1000 to 300000 carbon fibers with a fiberdiameter of 1 to 45 μm/fiber, the fibers being bundled so that an endface of the carbon fiber bundle 14 has a width L2 of 1.0 to 20.0 mm anda thickness L3 of 0.001 to 6.0 mm, where L2 is longer than L3.

As shown above, in this example, the carbon fiber bundle 14 is formed bybundling 1000 to 300000 carbon fibers with a fiber diameter of 1 to 45μm/fiber. This produces the suppressive effect of the carbon fiberbundles 14 on the development of a crack at the portion where the carbonfiber bundles 14 are placed and increases the bending strength andfracture energy of the magnesia carbon refractory 10. By contrast, whenthe carbon fibers have a fiber diameter of less than 1 μm/fiber, and thenumber of carbon fibers is less than 1000, the carbon fiber bundle istoo narrow to prevent the development of a crack and to increase thebending strength and fracture energy. When the carbon fibers have afiber diameter of more than 45 μm/fiber, and the number of carbon fibersis more than 300000, the carbon fiber bundle is so thick thatentanglements between the carbon fiber bundles and the refractory rawmaterial deteriorate, thus causing spring back during pressing andmaking the pressing difficult. The carbon fiber bundle 14 may be formedby bundling 1000 to 60000 carbon fibers.

The carbon fiber bundle 14 is preferably formed by bonding a bundle ofthe carbon fiber with at least one adhesive selected from a phenolicresin, an epoxy resin, a melamine resin, a urea resin, an alkyd resin,an unsaturated polyester resin, polyurethane, thermosetting polyimide,an alumina sol, a silica sol, a zirconia sol, a chromia sol, a titaniasol, a magnesia sol, a calcia sol, an yttria sol, pitch, tar, and astarch paste. Bonding a bundle of carbon fiber can improve adhesionbetween the carbon fibers and adhesion between the carbon fiber bundleand the refractory raw material, densify the pressed product, andthereby increase the bending strength and fracture energy of themagnesia carbon refractory 10.

The width L2 of an end face of the carbon fiber bundle 14 is longer thanthe thickness L3 of the end face. Such a flat shape with the width L2 ofan end face of the carbon fiber bundle 14 being longer than thethickness L3 of the end face can impart anisotropy to the bendingstrength of the carbon fiber bundle 14. When the carbon fiber bundles 14with such anisotropic bending strength are unidirectionally placedwithin the refractory, the magnesia carbon refractory 10 also hasanisotropic bending strength.

The magnesia carbon refractory 10 is a refractory produced by beingpress-formed in the direction perpendicular to the pressing surface 16.As illustrated in FIGS. 1(a) and 1(b), the carbon fiber bundles 14 areplaced such that the longitudinal directions of end faces of the carbonfiber bundles 14 are the same and the angle θ1 between the pressingsurface 16 and the longitudinal direction of each end face is 90degrees. In FIG. 1(b), the dotted line 18 is a line parallel to thepressing surface 16 drawn to indicate the angle θ1 between the pressingsurface 16 and the longitudinal direction of end faces of the carbonfiber bundles 14.

When the carbon fiber bundles 14 are placed in this manner such that thelongitudinal direction of end faces of the carbon fiber bundles 14 arethe same and the angle θ1 between the longitudinal direction of each endface and the pressing surface 16 is 90 degrees, this enables themagnesia carbon raw material 12 to easily enter between the carbon fiberbundles 14 during pressing and thereby improves formability of themagnesia carbon refractory 10. Furthermore, placing the carbon fiberbundles 14 such that the longitudinal directions of the end faces arethe same also imparts anisotropy to the bending strength of the magnesiacarbon refractory 10, and placing the carbon fiber bundles 14 such thatthe angle θ1 between each longitudinal direction and the pressingsurface 16 is 90 degrees can increase the bending strength in thelongitudinal direction of the end faces of the carbon fiber bundles 14compared to the bending strength in the longitudinal direction of theend faces of the carbon fiber bundles 14 in the magnesia carbonrefractory 10. Although the angle θ1 between the longitudinal directionand the pressing surface 16 is preferably 90 degrees, the angle θ1 maybe approximately 90±45 degrees in consideration of precision inworkability.

FIG. 3 is a schematic perspective view of the magnesia carbon refractory10 used as a converter refractory. As illustrated in FIG. 3, when themagnesia carbon refractories 10 are used in a converter, the magnesiacarbon refractories 10 are placed such that the direction of thepressing surfaces 16 is along the circumferential direction of theconverter (the arrow 20 in FIG. 3). In this example, the magnesia carbonrefractory 10 expands and contracts repeatedly due to sudden temperaturechanges in the operation of the converter, thereby causing stress in thecircumferential direction, that is, in the direction perpendicular tothe pressing surfaces 16.

As described above, the magnesia carbon refractory 10 according to thisexample has anisotropic bending strength, and the bending strengthperpendicular to the pressing surface 16 is higher than the bendingstrength parallel to the pressing surface 16. Thus, the magnesia carbonrefractories 10 have the pressing surfaces 16 whose direction is alongthe circumferential direction in which stress is caused in the converterand thereby have high bending strength against the stress caused in theconverter. Placing the magnesia carbon refractory 10 with anisotropicbending strength such that the direction in which the bending strengthis higher is the stress direction in the converter can improve thedurability of the magnesia carbon refractory 10.

As illustrated in FIGS. 1(a) and 1(b), the magnesia carbon refractory 10according to this example is placed such that the angle θ2 between thedirection perpendicular to the pressing surface 16 of the magnesiacarbon refractory 10 and the direction along the length L1 of the carbonfiber bundle 14 is 90 degrees. The bending strength and fracture energyof the magnesia carbon refractory 10 toward the force in the directionperpendicular to the pressing surface 16 are higher when the carbonfiber bundles 14 are placed in this way than when the carbon fiberbundles 14 are placed such that the direction perpendicular to thepressing surface 16 is parallel to the direction along the length L1 ofthe carbon fiber bundle 14.

FIGS. 4(a) and 4(b) include a perspective view and a side view of themagnesia carbon refractory 10 in which the angle θ2 between thedirection perpendicular to the pressing surface 16 of the magnesiacarbon refractory 10 and the direction along the length L1 of the carbonfiber bundle 14 is 45 degrees. FIGS. 5(a) and 5(b) include a perspectiveview and a side view of the magnesia carbon refractory 10 in which theangle θ2 between the direction perpendicular to the pressing surface 16of the magnesia carbon refractory 10 and the direction along the lengthL1 of the carbon fiber bundle 14 is 135 degrees. As illustrated in FIGS.4(a) and 4(b) and 5(a) and 5(b), the carbon fiber bundles 14 arepreferably placed such that the angle θ2 between the directionperpendicular to the pressing surface 16 of the magnesia carbonrefractory 10 and the direction along the length L1 of the carbon fiberbundle 14 is 45 to 135 degrees. This can increase the bending strengthand fracture energy of the magnesia carbon refractory 10 compared towhen the carbon fiber bundles 14 are placed such that the directionperpendicular to the pressing surface 16 of the magnesia carbonrefractory 10 is parallel to the direction along the length L1 of thecarbon fiber bundle 14. Although the carbon fiber bundles 14 areparallel to each other and are parallel to the face AEHD in FIGS. 4(a)and 4(b) and 5(a) and 5(b), the bending strength and fracture energy ofthe magnesia carbon refractory 10 are increased as long as the angles θ1and θ2 are 45 to 135 degrees even if the carbon fiber bundles 14 are notparallel to each other.

The magnesia carbon refractory 10 may further contain short carbonfibers constituting 0.10% to 10% by mass based on 100% by mass of themagnesia carbon raw material 12. The short carbon fibers have a fiberdiameter of 1 to 45 μm/fiber, a fiber length of 1 mm or less, and aratio of fiber length to fiber diameter (fiber length/fiber diameter) of2 to 1000. The short carbon fibers restrict the development of a crackin the magnesia carbon refractory 10 and thereby increase the bendingstrength and fracture energy of the magnesia carbon refractory 10.

FIG. 6 is a production flow diagram of the magnesia carbon refractory 10according to the example. A method of producing the magnesia carbonrefractory 10 is described below with reference to FIG. 6. The magnesiacarbon refractory 10 is produced through a carbon fiber bundling step, amagnesia carbon raw material 12 mixing step, a magnesia carbon rawmaterial 12 kneading step, a filling step, a pressing step, and a dryingstep.

In the carbon fiber bundling step (S101), for example, a commerciallyavailable carbon fiber fabric with a carbon fiber diameter of 1 μm/fiberor more and 45 μm or less is first defibrated to remove thread-likecarbon fibers 100 mm or more in length. Commercially available carbonfibers include carbon fibers of various shapes such as carbon fiberfilaments, carbon fiber tows, and carbon fiber cloth. Any of such carbonfibers may be used. Substantially, 1000 to 300000 of the thread-likecarbon fibers are bundled to prepare a carbon fiber bundle 100 mm ormore in length. The carbon fiber bundle is then immersed in an adhesivesuch as a phenolic resin for approximately 1 to 2 minutes. The carbonfiber bundle is removed from the adhesive such as a phenolic resin andair-dried for 24 hours or more.

In the magnesia carbon raw material 12 mixing step (S102), the magnesiacarbon raw material 12 is prepared by mixing graphite and the magnesiaraw material together such that the graphite content of the magnesiacarbon raw material 12 is 1% to 80% by mass, and the magnesia rawmaterial content of the magnesia carbon raw material 12 is 20% to 99% bymass. In the mixing step, predetermined amounts of a curing agent and abinder are added on an outer percentage basis.

In the mixing step, in addition to the graphite, short carbon fiberswith a fiber diameter of 1 to 45 μm, a fiber length of 1 mm or less, anda ratio of fiber length to fiber diameter (fiber length/fiber diameter)of 2 to 1000 may be further mixed with the magnesia carbon raw material12.

In the magnesia carbon raw material 12 kneading step (S103), themagnesia carbon raw material 12 is kneaded in a kneader. In the fillingstep (S104), 5% or more by volume of the mold of the refractory isfilled with the kneaded magnesia carbon raw material 12, and the carbonfiber bundles 14 are then placed at intervals of 3 mm or more.Subsequently, 5% or more by volume of the mold is filled with thekneaded magnesia carbon raw material 12, and the carbon fiber bundles 14are then placed at intervals of 3 mm or more. Filling with the magnesiacarbon raw material 12 and placing the carbon fiber bundles 14 arerepeatedly performed to fill the mold with the magnesia carbon rawmaterial 12 and the carbon fiber bundles 14.

Thus, placing the carbon fiber bundles 14 side by side at intervals of 3mm or more and repeatedly performing filling with the magnesia carbonraw material 12 and placing the carbon fiber bundles to distributecarbon fibers in the transverse direction and in the height method canincrease the contact area between the magnesia carbon raw material 12and the carbon fiber bundles and thereby increase the bending strengthand fracture energy of the magnesia carbon refractory. By contrast, whencarbon fiber bundles are placed to not be distributed in the transverseand height directions, the contact area between the magnesia carbon rawmaterial 12 and the carbon fiber bundles cannot be increased, andtherefore the bending strength and fracture energy of the magnesiacarbon refractory 10 cannot be increased. The carbon fiber bundles 14are preferably placed at intervals of 100 mm or less. When the carbonfiber bundles 14 are placed at intervals of more than 100 mm, number ofthe carbon fiber bundles 14 placed is so small that the effects ofincreasing the bending strength and fracture energy are reduced.

After the magnesia carbon raw material 12 is kneaded in the kneadingstep, the carbon fiber bundles 14 are preferably placed on the kneadedmagnesia carbon raw material 12 in the filling step. If the kneadingstep is performed after the carbon fiber bundles 14 are placed, thecarbon fiber bundles 14 are cut by impeller blades of the kneader, andthe effects of increasing the bending strength and fracture energy ofthe magnesia carbon refractory are undesirably reduced.

In the pressing step (S105), the refractory is pressed in the directionperpendicular to the pressing surface 16 to transfer the internal shapeof the mold to the magnesia carbon raw material 12 charged in the moldof the refractory, thereby pressing the pressed product. The mold may bea metal, wood, synthetic resin, or rubber mold. The pressed product isdried at 230° C. for 18 hours in the drying step (S106) to complete themagnesia carbon refractory 10 within which the carbon fiber bundles 14are placed.

Although the magnesia raw material is used as a refractory raw materialin this example, instead of the magnesia raw material, an alumina rawmaterial and a silicon carbide raw material may be used, or an aluminaraw material, a silicon carbide raw material, and a silica raw materialmay be used. When an alumina raw material and a silicon carbide rawmaterial are used, the alumina raw material constitutes 10% to 95% bymass of the graphite-containing refractory raw material, and the siliconcarbide raw material constitutes 1% or more by mass of thegraphite-containing refractory raw material. When an alumina rawmaterial, a silicon carbide raw material, and silica raw material areused, the alumina raw material constitutes 10% to 95% by mass of thegraphite-containing refractory raw material, the silicon carbide rawmaterial constitutes 1% or more by mass of the graphite-containingrefractory raw material, and the silica raw material constitutes 1% to50% by mass of the graphite-containing refractory raw material.

The alumina raw material constituting 10% to 95% by mass can improveerosion resistance to molten iron preliminary treatment slag and preventcracking caused by thermal spalling. By contrast, the alumina rawmaterial constituting less than 10% by mass undesirably results in lowererosion resistance to molten iron preliminary treatment slag. Thealumina raw material constituting more than 95% by mass cannot preventcracking caused by thermal spalling and undesirably results in decreasedcrack resistance.

The silicon carbide raw material constituting 1% or more by mass canprevent oxidation of graphite in the air and maintain high crackresistance of the graphite-containing refractory. By contrast, thesilicon carbide raw material constituting less than 1% by mass cannotprevent oxidation of graphite in the air and undesirably results indecreased crack resistance of the graphite-containing refractory.

The silica raw material constituting 1% to 50% by mass can impart bothhigh crack resistance and high erosion resistance to thegraphite-containing refractory. By contrast, the silica raw materialconstituting less than 1% by mass cannot increase thermal shock fractureresistance due to small expansion and no formation of microcracks,undesirably resulting in decreased crack resistance. The silica rawmaterial constituting more than 50% by mass undesirably results insignificantly decreased erosion resistance.

Thus, an alumina raw material and a silicon carbide raw material, or analumina raw material, a silicon carbide raw material, and a silica rawmaterial, mixed with graphite can improve the erosion resistance tomolten iron preliminary treatment slag of the graphite-containingrefractory and increase the bending strength and fracture energy of thegraphite-containing refractory. Thus, the refractory can suitably beused as a refractory liner for molten iron preliminary treatment vesselssuch as torpedoes and hot metal ladles.

Although the magnesia raw material is used as a refractory raw materialin this example, instead of the magnesia raw material, an alumina rawmaterial and a zirconia raw material may be used. Placing the carbonfiber bundles in a plate refractory containing an alumina raw material,a zirconia raw material, and graphite can also increase the bendingstrength and fracture energy of the plate refractory.

Although the magnesia raw material is used as a refractory raw materialin this example, instead of the magnesia raw material, a refractorywaste produced by crushing a used alumina-silicon carbide-carbonrefractory may be used. When a refractory waste is used, the refractorywaste constitutes 10% to 90% by mass of the graphite-containingrefractory raw material. This can achieve almost the same crackresistance and erosion resistance as a graphite-containing refractorymade of an unused virgin raw material alone.

Although refractory waste raw materials composed of refractory wasteshave a lower purity than virgin raw materials, a virgin raw materialconstituting 10% or more by mass of a refractory waste can suppress thesignificant decrease in erosion resistance caused by an Al₂O₃ componentin the refractory raw material. By contrast, a refractory waste rawmaterial constituting more than 90% by mass cannot reduce thesignificant decrease in erosion resistance of an Al₂O₃ component in therefractory waste raw material due to an excessively small amount ofvirgin raw material. A refractory waste raw material constituting lessthan 10% by mass results in a significant increase in treatment cost ofrefractory waste as industrial waste due to an excessively low reuserate of the refractory waste.

Although the mold is filled with the graphite-containing refractory rawmaterial and the carbon fiber bundles 14 to form a pressed product, ourmethods and refractories are not limited to this example. For example, apressed product may be formed by CIP pressing using a pressing vesselillustrated in FIGS. 7(a) and 7(b). FIGS. 7(a) and 7(b) includeexplanatory views of a pressing method by CIP pressing. FIG. 7(a)illustrates a pressing vessel 36 filled with the magnesia carbon rawmaterial 12 and the carbon fiber bundles 14, and FIG. 7(b) illustratesthe pressing vessel 36 in a CIP apparatus 38 filled with a pressuremedium 40.

First, a method of filling the pressing vessel 36 with the magnesiacarbon raw material 12 and the carbon fiber bundles 14 is describedbelow. In a supporting member 30 including a core metal 32, an uppersupporting plate 34, and a lower supporting plate 35, the carbon fiberbundles 14 extend parallel to the core metal 32 between the uppersupporting plate 34 and the lower supporting plate 35. The supportingmember 30 in which the carbon fiber bundles 14 extend is placed in thepressing vessel 36 made of rubber. The space formed by the supportingmember 30 and the pressing vessel 36 is filled with the magnesia carbonraw material 12, and the opening of the pressing vessel 36 is closed tohermetically seal the pressing vessel 36. The hermetically sealedpressing vessel 36 is placed in the CIP apparatus 38 filled with thepressure medium 40 such as water or oil, and a pressure of 49 to 490 MPais applied to the pressure medium 40. This enables a uniform pressure tobe applied to the pressing vessel 36 via the pressure medium 40, therebypressing a pressed product. CIP pressing is preferably used to form alarge tuyere refractory. The length of the core metal 32, the diameterof the core metal 32, the sizes of the upper supporting plate 34 and thelower supporting plate 35, and the size of the pressing vessel 36 can beappropriately determined according to the desired size such as tuyerediameter, of the tuyere refractory. For CIP pressing, the pressingvessel 36 is preferably made of a rubber material.

EXAMPLES

Examples are described below. A graphite-containing refractorycontaining, as an aggregate, a magnesia carbon raw material for use in aconverter was examined by the following method. First, to study themagnesia raw material and graphite contents, the magnesia raw materialcontent and the graphite content were changed as listed in Table 1, anda graphite-containing refractory was produced according to the flowdiagram of FIG. 6. The erosion resistance and the crack resistance wereevaluated.

TABLE 1 Mixture Mixture Mixture Mixture Mixture Mixture Mixture MixtureMixture example example example example example example example exampleexample Particle size (mm) Unit 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 MgO3-5 mass % 11.7 11.6 11.2 10.0 9.4 7.1 4.7 2.4 1.2 1 or more and 35.134.9 33.5 30.0 28.2 21.2 14.1 7.1 3.5 less than 3 0.3 or more and 35.134.9 33.5 30.0 28.2 21.2 14.1 7.1 3.5 less than 1 50-200 Mesh 17.6 17.516.8 15.0 14.1 10.6 7.1 3.5 1.8 (0.075 or more and less than 0.3) Flakegraphite — 0.5 1.0 5.0 15.0 20.0 40.0 60.0 80.0 90.0 Metallic Si — mass% 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 powder (outer Hexamine —percentage) 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Phenolic resin — 3 3 3 33 3 3 3 3 Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0 100.0Erosion resistance — 97 98 99 100 103 105 107 109 140 Crack resistanceE₃/E₀ 0.10 0.40 0.41 0.41 0.42 0.43 0.44 0.45 0.45

Erosion resistance was determined by a lining partitioning method in ahigh-frequency induction furnace illustrated in FIGS. 8(a) and 8(b).

FIGS. 8(a) and 8(b) include schematic cross-sectional views illustratingan erosion test in a high-frequency induction furnace 50. As illustratedin FIGS. 8(a) and 8(b), graphite-containing refractories 60 werecylindrically placed on a bottom plate 54 of the high-frequencyinduction furnace 50 equipped with an induction coil 52. The testtemperature was 1500° C., and the temperature holding time was 4 hours.Molten iron 56 or synthetic slag 58 with a composition listed in Table 2was poured into the high-frequency induction furnace 50 every hour.After cooling, the amount of erosion was measured. The erosionresistance in Table 1 was indicated by the erosion index in which theamount of erosion of a mixture example 1-3 was set at 100. Thus, anerosion index of less than 100 means that the amount of erosion issmaller than that of the mixture example 1-3, and an erosion index ofmore than 100 means that the amount of erosion is larger than that ofthe mixture example 1-3.

TABLE 2 Slag composition (mass %) CaO SiO₂ FeO 30 40 30

For crack resistance, the dynamic elastic modulus E₀ in the longitudinaldirection of a 40×40×200 mm specimen was determined by an ultrasonicpulse method specified in Japanese Industrial Standards (JIS) R 1605. Aspalling test consisting of a cycle of heating at 1500° C. for 10minutes, water cooling for 5 minutes, and air-cooling for 10 minutes wasperformed three times. Subsequently, the dynamic elastic modulus E₃ wasmeasured again. The ratio of change in dynamic elastic modulus E_(3/)E₀resulting from the test was determined to evaluate crack resistance. Asmaller ratio of change in dynamic elastic modulus E₃/E₀ means lowercrack resistance.

Table 1 shows that the mixture examples 1-2 to 1-8 with a graphitecontent of 1% to 80% by mass and a magnesia raw material content of 20%to 99% by mass had constant erosion resistance and crack resistance. Bycontrast, the mixture example 1-1 with a graphite content of 0.5% bymass had significantly decreased crack resistance, and the mixtureexample 1-9 with a magnesia raw material content of 10.0% by mass hadsignificantly decreased erosion resistance. These results show that whenthe magnesia raw material was used as a refractory raw material, agraphite content of 1% to 80% by mass and a magnesia raw materialcontent of 20% to 99% by mass resulted in both high erosion resistanceand high crack resistance of the graphite-containing refractory.

The following describes the effects of the length of carbon fiberbundles on the bending strength, breaking strength, erosion resistance,and crack resistance of a graphite-containing refractory. Table 3 showsthe production conditions and evaluation results of testedgraphite-containing refractories.

TABLE 3 Com- parative example Example Example Example Example ExampleExample Example Unit 2-1 2-1 2-2 2-3 2-4 2-5 2-6 2-7 Carbon Fiber shapeLength mm 90 100 100 200 400 600 800 1000 fibers Diameter μm/fiber 0.8 11 7 Number of fiber 990 990 1,000 12,000 bundled fibers PreliminaryPhenolic resin Done treatment bonding Charging Initial charging Vol % 10method amount of refractory raw material relative to mold volume Secondand later Vol % 15 charging amounts of refractory raw material relativeto mold volume Angle of placement ° 90 of carbon fiber bundle (θ2)Intervals between mm 5 carbon fiber bundles Repetition of Yes chargingof raw material and placement of carbon fiber bundles Timing of placingcarbon After kneading raw materials fiber bundles Bending strength MPa7.0 18.4 18.5 18.6 18.7 19.0 18.8 12.5 Fracture energy kJ/m² 0.8 19 2021 21 22 23 23 Erosion resistance — 100 100 100 101 101 101 101 101Crack resistance E₃/E₀ 0.35 0.49 0.50 0.51 0.51 0.53 0.52 0.51

As shown in Table 3, when 990 to 12000 carbon fibers with a fiberdiameter of 0.8 to 7 μm/fiber were bundled such that the carbon fiberbundle 14 had a flat end face, the end face of the carbon fiber bundle14 had a width of 1.0 to 20.0 mm and a thickness of 0.001 to 10.0 mm.TORAYCA (registered trademark) product number CK6261C manufactured byToray Industries, Inc. was defibrated and used as the carbon fibers. Thecarbon fiber bundles were cut to 90, 100, 200, 400, 600, 800, or 1000 mmin length. To improve adhesion between carbon fibers and adhesionbetween the carbon fiber bundles and the magnesia carbon raw material,the carbon fiber bundles were immersed in a phenolic resin for 1 minuteto adhere closely to the phenolic resin, and then the carbon fiberbundles and the magnesia carbon raw material were charged by thefollowing method.

A lower part of a mold for a refractory 1000 mm in the longitudinaldirection, 300 mm in the transverse direction, and 90 mm in height wasfilled with a magnesia carbon raw material amounting 10% by volume ofthe mold. The carbon fiber bundles were placed at intervals of 5 mm suchthat the angle θ2 between the direction perpendicular to the pressingsurface and the direction along the length L1 of the carbon fiber bundlewas 90 degrees. The magnesia carbon raw material with which the mold wasfilled was the magnesia carbon raw material of the mixture example 1-5listed in Table 1.

Filling with the magnesia carbon raw material and placing the carbonfiber bundles were repeatedly performed to fill the mold with themagnesia carbon raw material and the carbon fiber bundles. Aftercompletion of filling, pressing and drying were performed according tothe flow diagram of FIG. 6 to prepare graphite-containing refractoriesaccording to Examples 2-1 to 2-7 and Comparative Example 2-1. Thebending strength, fracture energy, erosion resistance, and crackresistance of the graphite-containing refractories were determined.

The bending strength of the graphite-containing refractory wasdetermined by the three-point bending test method according to JapaneseIndustrial Standards (JIS) R 2213. The test specimen size was 40×40×140mm, the center-to-center distance was 100 mm, and the loading speed was0.5 mm/min.

FIG. 9 is a load-displacement curve obtained by the three-point bendingtest method. The fracture energy can be calculated from theload-displacement curve obtained by the three-point bending test method.The displacement of the first peak value on the load-displacement curvewas taken as the reference position, and the area between the referenceposition and the displacement of 1 mm from the reference position wascalculated as fracture energy.

As shown in Table 3, the graphite-containing refractories according toExamples 2-1 to 2-7 containing the carbon fiber bundles 100 mm or morein length had very high bending strength and fracture energy. Bycontrast, the graphite-containing refractory according to ComparativeExample 2-1 containing carbon fiber bundles less than 100 mm in lengthhad lower bending strength and fracture energy than thegraphite-containing refractories according to Examples 2-1 to 2-7. Thisis probably because the graphite-containing refractory according toComparative Example 2-1 contained short carbon fiber bundles andtherefore had no suppressive effect of the carbon fiber bundles on thedevelopment of a crack in the refractory. These results show that thelength of carbon fibers is 100 mm or more to increase the bendingstrength and fracture energy of the graphite-containing refractory.

The following describes the effects of the carbon fiber diameter and thenumber of carbon fiber bundles on the bending strength, breakingstrength, erosion resistance, and crack resistance of agraphite-containing refractory. Table 4 shows the production conditionsand evaluation results of tested graphite-containing refractories.

TABLE 4 Com- Com- parative parative example Example Example ExampleExample Example Example example Unit 3-1 3-1 3-2 2-5 3-3 3-4 3-5 3-2Carbon Fiber shape Length mm 600 90 fibers Diameter μm/fiber 1 1 1 7 2345 45 50 Number of bundled fibers fiber 900 1,000 10,000 12,000 30,00060,000 300,000 400,000 Preliminary Phenolic resin bonding Done treatmentCharging Initial charging amount of Vol % 10 method refractory rawmaterial relative to mold volume Second and later charging Vol % 15amounts of refractory raw material relative to mold volume Angle ofplacement of ° 90 carbon fiber bundle (θ2) Intervals between carbon mm 5 fiber bundles Repetition of charging of Yes raw material andplacement of carbon fiber bundles Timing of placing carbon fiber bundlesAfter kneading raw materials Bending strength MPa 11.5 17.9 18.5 19.018.8 18.7 19.0 Difficult Fracture energy kJ/m² 10 20 21 22 22 22 22 toform Erosion resistance — 102 102 101 101 101 101 101 Crack resistanceE₃/E₀ 0.45 0.52 0.51 0.53 0.52 0.51 0.54

As shown in Table 4, the graphite-containing refractories according toExamples 3-1 to 3-5 and Comparative Examples 3-1 and 3-2 aregraphite-containing refractories in which carbon fiber bundles eachcomposed of 900, 1000, 10000, 12000, 30000, 60000, 300000, or 400000carbon fibers with a length of 600 mm and a fiber diameter of 1, 7, 23,45, or 50 μm/fiber are placed. The raw material components of thesegraphite-containing refractories are the same as those in the mixtureexample 1-5, and the size of each graphite-containing refractory is thesame as that in Example 2-1. The bending strength, fracture energy,erosion resistance, and crack resistance of the graphite-containingrefractories according to Examples 3-1 to 3-5 and Comparative Examples3-1 and 3-2 were determined.

As shown in Table 4, the graphite-containing refractories according toExamples 3-1 to 3-5 and Example 2-5 containing carbon fiber bundles eachcomposed of 1000 to 300000 carbon fibers with a fiber diameter of 1 to45 μm/fiber had high bending strength and fracture energy. By contrast,the graphite-containing refractory according to Comparative Example 3-1containing carbon fiber bundles each composed of less than 1000 carbonfibers with a fiber diameter of less than 1 μm/fiber had lower bendingstrength and fracture energy than the graphite-containing refractoriesaccording to Example 2-5 and Examples 3-1 to 3-5. Thegraphite-containing refractory according to Comparative Example 3-2containing carbon fiber bundles each composed of more than 300000, morespecifically 400000, carbon fibers with a fiber diameter of more than 45μm/fiber, more specifically 50 μm/fiber, underwent lamination duringpressing and was difficult to be pressed due to carbon fiber bundlesprotruding from a side surface of the refractory. This is probablybecause the carbon fiber bundles were too thick to be entangled with themagnesia carbon raw material and caused spring back during pressing.These results show that carbon fiber bundles each composed of 1000 to300000 carbon fibers with a fiber diameter of 1 to 45 μm/fiber can beused to increase the bending strength and fracture energy of thegraphite-containing refractory.

The following describes the effects of the presence or absence ofadhesion in carbon fiber bundles on the bending strength, breakingstrength, erosion resistance, and crack resistance of agraphite-containing refractory. Table 5 shows the production conditionsand evaluation results of tested graphite-containing refractories.

TABLE 5 Example Example Example Example Example Example Example Unit 2-54-1 4-2 4-3 4-4 4-5 4-6 Carbon Fiber shape Length mm 600 fibers Diameterμm/fiber 7 Number of fiber 12,000 bundled fibers Preliminary Phenolicresin ◯ — — — — — ◯ treatment Alumina sol — ◯ — — — — ◯ (bonding) Silicasol — — ◯ — — — — Pitch — — — ◯ — — — Tar — — — — ◯ — — Starch paste — —— — — ◯ — Charging Initial charging Vol % 10 method amount of refractoryraw material relative to mold volume Second and later Vol % 15 chargingamounts of refractory raw material relative to mold volume Angle ofplacement ° 90 of carbon fiber bundle (θ2) Intervals between mm 5 carbonfiber bundles Repetition of Yes charging of raw material and placementof carbon fiber bundles Timing of placing carbon After kneading rawmaterials fiber bundles Bending strength MPa 19.0 19.1 18.9 18.6 18.418.5 19.4 Fracture energy kJ/m² 22 22 21 20 20 20 24 Erosion resistance— 101 101 101 101 101 101 101 Crack resistance E₃/E₀ 0.53 0.52 0.54 0.510.50 0.51 0.56 Example Example Example Example Example 4-7 4-8 4-9 4-104-11 Carbon Fiber shape Length mm 600 fibers Diameter μm/fiber 7 Numberof fiber 12,000 bundled fibers Preliminary Phenolic resin ◯ ◯ ◯ ◯ —treatment Alumina sol — — — — — (bonding) Silica sol ◯ — — — — Pitch — ◯— — — Tar — — ◯ — — Starch paste — — — ◯ — Charging Initial charging Vol% 10 method amount of refractory raw material relative to mold volumeSecond and later Vol % 15 charging amounts of refractory raw materialrelative to mold volume Angle of placement ° 90 of carbon fiber bundle(θ2) Intervals between mm 5 carbon fiber bundles Repetition of Yescharging of raw material and placement of carbon fiber bundles Timing ofplacing carbon After kneading raw materials fiber bundles Bendingstrength MPa 19.4 19.3 19.3 19.3 12.4 Fracture energy kJ/m² 24 23 23 2310 Erosion resistance — 101 101 101 101 101 Crack resistance E₃/E₀ 0.560.55 0.55 0.55 0.45

As shown in Table 5, the graphite-containing refractories according toExamples 4-1 to 4-11 are graphite-containing refractories in whichcarbon fiber bundles each composed of 12000 carbon fibers 600 mm inlength and 7 μm/fiber in diameter bonded together by using a phenolicresin, an alumina sol, a silica sol, pitch, tar, or a starch paste as anadhesive or carbon fiber bundles each composed of the carbon fibers notbonded together are placed. The raw material components of thesegraphite-containing refractories are the same as those in the mixtureexample 1-5, the size of each graphite-containing refractory is the sameas that in Example 2-1, and the production method is the same as themethod described in Table 3. The bending strength, fracture energy,erosion resistance, and crack resistance of the graphite-containingrefractories according to Examples 4-1 to 4-11 were determined.

As shown in Table 5, the graphite-containing refractories according toExamples 2-5 and 4-1 to 4-5 containing carbon fiber bundles with bondingby a phenolic resin, an alumina sol, a silica sol, pitch, tar, or astarch paste had high bending strength and fracture energy. Thegraphite-containing refractories according to Examples 4-6 to 4-10containing carbon fiber bundles with bonding by a phenolic resin and analumina sol, a phenolic resin and a silica sol, a phenolic resin andpitch, a phenolic resin and tar, or a phenolic resin and a starch pastehad high bending strength and fracture energy.

The graphite-containing refractory according to Example 4-11 containingcarbon fiber bundles without bonding had lower bending strength andfracture energy than the graphite-containing refractories according toExample 2-5 and Examples 4-1 to 4-10. This is probably because eachcarbon fiber bundle with bonding improved the adhesion between carbonfibers and the adhesion between the carbon fiber bundles and themagnesia carbon raw material. These results show that carbon fibers arepreferably bonded together by using at least one adhesive selected froma phenolic resin, an alumina sol, a silica sol, pitch, tar, and a starchpaste to form a carbon fiber bundle to increase the bending strength andfracture energy of the graphite-containing refractory. We believe thatthe same effect can be achieved by using an epoxy resin, a melamineresin, a urea resin, an alkyd resin, an unsaturated polyester resin,polyurethane, thermosetting polyimide, a zirconia sol, a chromia sol, atitania sol, a magnesia sol, a calcia sol, or an yttria sol, which issimilar to the above adhesive.

The following describes the effects of the inclination of carbon fiberbundles on the bending strength, breaking strength, erosion resistance,and crack resistance of a graphite-containing refractory. Table 6 showsthe production conditions and evaluation results of testedgraphite-containing refractories.

TABLE 6 Example Example Example Example Unit 5-1 2-5 5-2 5-3 CarbonFiber shape Length mm 600 fibers Diameter μm/fiber 7 Number of bundledfibers fiber 12,000 Preliminary Phenolic resin bonding Done treatmentCharging Initial charging amount of Vol % 10 method refractory rawmaterial relative to mold volume Second and later charging Vol % 15amounts of refractory raw material relative to mold volume Angle ofplacement of carbon ° 45 90 135 0 fiber bundle (θ2) Intervals betweencarbon fiber mm 5 bundles Repetition of charging of raw Yes material andplacement of carbon fiber bundles Timing of placing carbon fiber bundlesAfter kneading raw materials Bending strength MPa 18.0 19.0 18.1 12.2Fracture energy kJ/m² 20 22 21 11 Erosion resistance — 101 101 101 101Crack resistance E₃/E₀ 0.51 0.53 0.52 0.46

As shown in Table 6, the graphite-containing refractories according toExamples 5-1 to 5-3 are graphite-containing refractories in which carbonfiber bundles each composed of 12000 carbon fibers 600 mm in length and7 μm/fiber in diameter are placed at an angle θ2 of 0, 45, 90, or 135degrees to the transverse direction of the refractories. The rawmaterial components of these graphite-containing refractories are thesame as those in the mixture example 1-5, the size of eachgraphite-containing refractory is the same as that in Example 2-1, andthe production method is the same as the method described in Table 3.

A graphite-containing refractory in which carbon fiber bundles areplaced at an angle θ2 of 90 degrees to the transverse direction of therefractory corresponds to a graphite-containing refractory illustratedin FIGS. 1(a) and 1(b). A graphite-containing refractory in which carbonfiber bundles are placed at an angle θ2 of 45 degrees corresponds to agraphite-containing refractory illustrated in FIGS. 4(a) and 4(b). Agraphite-containing refractory in which carbon fiber bundles are placedat an angle θ2 of 135 degrees corresponds to a graphite-containingrefractory illustrated in FIGS. 5(a) and 5(b). The bending strength,fracture energy, erosion resistance, and crack resistance of thegraphite-containing refractories according to Examples 5-1 to 5-3 weredetermined.

As shown in Table 6, the graphite-containing refractory according toExample 2-5 in which carbon fiber bundles were placed at an angle θ2 of90 degrees to the transverse direction, the graphite-containingrefractory according to Example 5-1 in which carbon fiber bundles wereplaced at an angle θ2 of 45 degrees to the transverse direction, and thegraphite-containing refractory according to Example 5-2 in which carbonfiber bundles were placed at an angle θ2 of 135 degrees to thetransverse direction had high bending strength and fracture energy. Bycontrast, the graphite-containing refractory according to Example 5-3 inwhich carbon fiber bundles were placed at an angle θ2 of 0 degrees tothe transverse direction had lower bending strength and fracture energythan the graphite-containing refractories according to Example 2-5 andExamples 5-1 and 5-2. These results show that carbon fiber bundles arepreferably placed at an angle θ2 of 45 to 135 degrees to the transversedirection of a graphite-containing refractory to increase the bendingstrength and fracture energy of the graphite-containing refractory.

The following describes the effects of the intervals of carbon fiberbundles on the bending strength, breaking strength, erosion resistance,and crack resistance of a graphite-containing refractory. Table 7 showsthe production conditions and evaluation results of testedgraphite-containing refractories.

TABLE 7 Example Example Example Example Unit 6-1 6-2 6-3 6-4 CarbonFiber shape Length mm 600 fibers Diameter μm/fiber 7 Number of bundledfibers fiber 12,000 Preliminary Phenolic resin bonding Done treatmentCharging Initial charging amount of Vol % 10 method refractory rawmaterial relative to mold volume Second and later charging Vol % 15amounts of refractory raw material relative to mold volume Angle ofplacement of carbon ° 90 fiber bundle (θ2) Intervals between carbonfiber mm 3 30 100 1 bundles Repetition of charging of raw Yes materialand placement of carbon fiber bundles Timing of placing carbon fiberbundles After kneading raw materials Bending strength MPa 19.5 18.1 18.010.8 Fracture energy kJ/m² 23 21 20 10 Erosion resistance — 101 101 101107 Crack resistance E₃/E₀ 0.57 0.53 0.51 0.43

As shown in Table 7, the graphite-containing refractories according toExamples 6-1 to 6-4 are graphite-containing refractories in which carbonfiber bundles each composed of 12000 carbon fibers 600 mm in length and7 μm/fiber in diameter are placed at intervals of 1, 3, 30, or 100 mm.The raw material components of these graphite-containing refractoriesare the same as those in the mixture example 1-5, the size of eachgraphite-containing refractory is the same as that in Example 2-1, andthe production method is the same as the method described in Table 3.The bending strength, fracture energy, erosion resistance, and crackresistance of the graphite-containing refractories according to Examples6-1 to 6-4 were determined.

As shown in Table 7, the graphite-containing refractories according toExamples 6-1 and 6-2 in which carbon fiber bundles were placed atintervals of 3 or 30 mm had slightly higher bending strength andfracture energy than the graphite-containing refractory according toExample 6-3 in which carbon fiber bundles were placed at intervals of100 mm. The graphite-containing refractory according to Example 6-4 inwhich carbon fiber bundles were placed at intervals of 1 mm tended toundergo lamination during pressing due to the excessively narrowintervals between the carbon fiber bundles. Thus, thegraphite-containing refractory according to Example 6-4 had decreasedbending strength and fracture energy as well as decreased erosionresistance and spalling resistance. The bending strength and fractureenergy when the intervals between carbon fiber bundles were 100 mm wereslightly lower than but almost the same as those when the intervalsbetween carbon fiber bundles were 3 to 30 mm. These results show thatthe intervals between carbon fiber bundles are preferably 3 to 100 mm,more preferably 3 to 30 mm, to increase the bending strength andfracture energy of the graphite-containing refractory.

The following describes the effects of the intervals of carbon fiberbundles in the pressing direction on the bending strength, breakingstrength, erosion resistance, and crack resistance of agraphite-containing refractory. Table 8 shows the production conditionsand evaluation results of tested graphite-containing refractories.

TABLE 8 Example Example Unit 2-5 7-1 Carbon Fiber shape Length mm 600fibers Diameter μm/fiber 7 Number of bundled fibers fiber 12,000Preliminary Phenolic resin bonding Done treatment Charging Initialcharging amount of refractory raw Vol % 10 method material relative tomold volume Second and later charging amounts of Vol % 15 refractory rawmaterial relative to mold volume Angle of placement of carbon fiberbundle ° 90 (θ2) Intervals between carbon fiber bundles mm 5 Repetitionof charging of raw material and Yes No placement of carbon fiber bundlesTiming of placing carbon fiber bundles After kneading raw materialsBending strength MPa 19.0 12.9 Fracture energy kJ/m² 22 12 Erosionresistance — 101 102 Crack resistance E₃/E₀ 0.53 0.47

As shown in Table 8, the graphite-containing refractory according toExample 7-1 is a graphite-containing refractory in which carbon fiberbundles each composed of 12000 carbon fibers 600 mm in length and 7μm/fiber in diameter are placed in a single layer instead of fillingwith the magnesia carbon raw material and placing the carbon fiberbundles being repeatedly performed. The raw material components of thisgraphite-containing refractory are the same as those in the mixtureexample 1-5, and the size of the graphite-containing refractory is thesame as that in Example 2-1. The bending strength, fracture energy,erosion resistance, and crack resistance of the graphite-containingrefractory were determined.

As shown in Table 8, the graphite-containing refractory according toExample 2-5 in which the carbon fiber bundles were layered had highbending strength and fracture energy. By contrast, thegraphite-containing refractory according to Example 7-1 in which thecarbon fiber bundles were placed in a single layer had lower bendingstrength and fracture energy. These results show that carbon fiberbundles are preferably layered by repeatedly performing filling with amagnesia carbon raw material and then placing the carbon fiber bundlesto increase the bending strength and fracture energy of thegraphite-containing refractory.

The following describes the effects of the timing of placing carbonfiber bundles on the bending strength, breaking strength, erosionresistance, and crack resistance of a graphite-containing refractory.Table 9 shows the production conditions and evaluation results of testedgraphite-containing refractories.

TABLE 9 Example Example Unit 8-1 8-2 Carbon Fiber shape Length mm 1,200fibers Diameter μm/fiber 7 Number of bundled fibers fiber 24,000Preliminary Phenolic resin bonding Done treatment Charging Initialcharging amount of refractory raw Vol % 10 method material relative tomold volume Second and later charging amounts of Vol % 15 refractory rawmaterial relative to mold volume Angle of placement of carbon fiberbundle ° 90 90 (θ2) Intervals between carbon fiber bundles mm 5Repetition of charging of raw material and Yes placement of carbon fiberbundles Timing of placing carbon fiber bundles After Before kneadingkneading raw raw materials materials Bending strength MPa 24.7 14.8Fracture energy kJ/m² 48 29 Erosion resistance — 101 101 Crackresistance E₃/E₀ 0.70 0.50

As shown in Table 9, the graphite-containing refractory according toExample 8-1 is a graphite-containing refractory produced by placingcarbon fiber bundles each composed of 24000 carbon fibers 1200 mm inlength and 7 μm/fiber in diameter on the magnesia carbon raw materialafter kneading. The graphite-containing refractory according to Example8-2 is a graphite-containing refractory produced by placing the samecarbon fiber bundles on the magnesia carbon raw material before kneadingand by subsequently kneading the magnesia carbon raw material. The rawmaterial components of these graphite-containing refractories are thesame as those in the mixture example 1-5, and the size of eachgraphite-containing refractory is the same as that in Example 2-1. Thebending strength, fracture energy, erosion resistance, and crackresistance of the graphite-containing refractories according to Examples8-1 and 8-2 were determined.

As shown in Table 9, the graphite-containing refractory according toExample 8-1 in which the carbon fiber bundles were placed on themagnesia carbon raw material after kneading had high bending strengthand fracture energy. By contrast, the graphite-containing refractoryaccording to Example 8-2 in which the carbon fiber bundles were mixedbefore kneading and were subsequently kneaded had lower bending strengthand fracture energy than the graphite-containing refractory according toExample 8-1. This is probably because kneading after placing carbonfiber bundles caused the carbon fiber bundles to be cut by impellerblades during kneading, and the decrease in fiber length resulted in asmaller suppressive effect of the carbon fiber bundles on thedevelopment of a crack. These results show that carbon fiber bundles arepreferably placed on a refractory raw material after kneading therefractory raw material and before the pressing step to increase thebending strength and fracture energy of the graphite-containingrefractory.

The following describes the effects of the angle of carbon fiber bundlesto the transverse direction on the bending strength, breaking strength,erosion resistance, and crack resistance of a graphite-containingrefractory produced by CIP pressing. Table 10 shows the productionconditions and evaluation results of tested graphite-containingrefractories.

TABLE 10 Example Example Example Example Unit 9-1 9-2 9-3 9-4 CarbonFiber shape Length mm 800 fibers Diameter μm/fiber 7 Number of bundledfibers fiber 24,000 Preliminary Phenolic resin bonding Done treatmentCharging Initial charging amount of Vol % 10 method refractory rawmaterial relative to mold volume Second and later charging Vol % 15amounts of refractory raw material relative to mold volume Angle ofplacement of carbon ° 45 90 135 5 fiber bundle (θ3) Intervals betweencarbon fiber mm 5 bundles Repetition of charging of raw Yes material andplacement of carbon fiber bundles Timing of placing carbon fiber bundlesAfter kneading raw materials Bending strength MPa 23.0 23.8 23.1 16.7Fracture energy kJ/m² 43 45 44 27 Erosion resistance — 101 101 101 101Crack resistance E₃/E₀ 0.65 0.67 0.66 0.58

FIGS. 10(a)-10(c) include schematic cross-sectional views illustratingthe placement angles of carbon fiber bundles in Examples 9-1 to 9-3. Asshown in Table 10 and FIGS. 10(a), (b), and (c), carbon fiber bundleseach composed of 2400 carbon fibers 800 mm in length and 7 μm/fiber indiameter being bonded by the same method as the bonding method describedin Table 3 were placed between the upper supporting plate 34 and thelower supporting plate 35 in the supporting member 30 such that theangle θ3 between the length direction of each carbon fiber bundle andthe transverse direction of each graphite-containing refractory was 45degrees (FIG. 10(b)), 90 degrees (FIG. 10(a)), 135 degrees (FIG. 10(c)),or 5 degrees and intervals of the bundles were 5 mm. The supportingmember 30 in which the carbon fiber bundles 14 were placed was put inthe pressing vessel 36. The space formed by the supporting member 30 andthe pressing vessel 36 was filled with the magnesia carbon raw material12. The opening was then closed to hermetically seal the pressing vessel36.

FIG. 11 is a schematic cross-sectional view of the pressing state in aCIP apparatus. As illustrated in FIG. 11, the hermetically sealedpressing vessel 36 was placed in the CIP apparatus 38 filled with thepressure medium 40 and was pressed via the pressure medium 40. After apressure was applied for a predetermined time, a pressed product wasremoved from the pressing vessel 36 to prepare the graphite-containingrefractories according to Examples 9-1 to 9-4. The raw materialcomponents of these graphite-containing refractories are the same asthose in the mixture example 1-5, and the size of eachgraphite-containing refractory is the same as that in Example 2-1. Thebending strength, fracture energy, erosion resistance, and crackresistance of the graphite-containing refractories according to Examples9-1 to 9-4 were determined.

As shown in Table 10, the graphite-containing refractories according toExamples 9-1 to 9-3 in which the angle θ3 was 45, 90, or 135 degrees tothe transverse direction of each graphite-containing refractory had highbending strength and fracture energy against the stress in thetransverse direction. By contrast, the graphite-containing refractoryaccording to Example 9-4 in which the angle θ3 was 5 degrees to thetransverse direction of the graphite-containing refractory had lowerbending strength and fracture energy against the stress in thetransverse direction than the graphite-containing refractories accordingto Examples 9-1 to 9-3. These results also show that in agraphite-containing refractory pressed by CIP pressing, carbon fiberbundles are preferably placed at an angle θ3 of 45 to 135 degrees to thetransverse direction of the graphite-containing refractory to increasethe bending strength and fracture energy of the graphite-containingrefractory.

The following describes the effects of the angle to the longitudinaldirection of each carbon fiber bundle on the bending strength, breakingstrength, erosion resistance, and crack resistance of thegraphite-containing refractories produced by CIP pressing, wherein thedirection in which the carbon fiber bundles were placed in thegraphite-containing refractories illustrated in FIGS. 10(a)-10(c) waschanged to the direction along the longitudinal direction of eachgraphite-containing refractory. Table 11 shows the production conditionsand evaluation results of tested graphite-containing refractories.

TABLE 11 Example Example Example Example Unit 10-1 10-2 10-3 10-4 CarbonFiber shape Length mm 1,200 fibers Diameter μm/fiber 7 Number of bundledfibers fiber 24,000 Preliminary Phenolic resin bonding Done treatmentCharging Initial charging amount of Vol % 10 method refractory rawmaterial relative to mold volume Second and later charging Vol % 15amounts of refractory raw material relative to mold volume Angle ofplacement of carbon ° 45 90 135 5 fiber bundle (θ4) Intervals betweencarbon fiber mm 5 bundles Repetition of charging of raw Yes material andplacement of carbon fiber bundles Timing of placing carbon fiber bundlesAfter kneading raw materials Bending strength MPa 24.1 24.7 24.2 17.3Fracture energy kJ/m² 47 48 46 29 Erosion resistance — 101 101 101 101Crack resistance E₃/E₀ 0.68 0.70 0.69 0.61

FIGS. 12(a)-12(c) include schematic cross-sectional views illustratingthe placement angles of carbon fiber bundles in Examples 10-1 to 10-3.Using a pressing vessel 1500 mm in the longitudinal direction, 150 mm inthe transverse direction, and 150 mm in height, as shown in Table 11 andFIGS. 12(a), (b), and (c), carbon fiber bundles each composed of 24000carbon fibers 1200 mm in length and 7 μm/fiber in diameter bonded by thesame method as the bonding method described in Table 3 were placedbetween the upper supporting plate 34 and the lower supporting plate 35such that the angle θ4 between the length direction of each carbon fiberbundle and the longitudinal direction of each graphite-containingrefractory was 45 degrees (FIG. 12(b)), 90 degrees (FIG. 12(a)), 135degrees (FIG. 12(c)), or 5 degrees and intervals between the bundleswere 5 mm. The supporting member 30 in which the carbon fiber bundles 14were thus placed was turned 90 degrees and was put in the pressingvessel 36. The space formed by the supporting member 30 and the pressingvessel 36 was filled with the magnesia carbon raw material 12. Theopening was then closed to hermetically seal the pressing vessel 36.

FIG. 13 is a schematic cross-sectional view of the pressing state in aCIP apparatus. As illustrated in FIG. 13, the hermetically sealedpressing vessel 36 was placed in the CIP apparatus 38 filled with thepressure medium 40 and was pressed via the pressure medium 40. After apressure was applied for a predetermined time, a pressed product wasremoved from the pressing vessel 36 to prepare the graphite-containingrefractories according to Examples 10-1 to 10-4. The raw materialcomponents of these graphite-containing refractories are the same asthose in the mixture example 1-5, and the size of eachgraphite-containing refractory is the same as that in Example 2-1. Thebending strength, fracture energy, erosion resistance, and crackresistance of Examples 10-1 to 10-4 were determined.

As shown in Table 11, the graphite-containing refractories according toExamples 10-1 to 10-3 in which the angle θ4 was 45, 90, or 135 degreesto the longitudinal direction of each graphite-containing refractory hadhigh bending strength and fracture energy against the stress in thelongitudinal direction. By contrast, the graphite-containing refractoryaccording to Example 10-4 in which the angle θ4 was 5 degrees to thelongitudinal direction of the graphite-containing refractory had lowerbending strength and fracture energy against the stress in thelongitudinal direction than the graphite-containing refractoriesaccording to Examples 10-1 to 10-3. These results show that the carbonfiber bundles 14 are preferably placed at an angle θ4 of 45 to 135degrees to the longitudinal direction of a graphite-containingrefractory to increase the bending strength and fracture energy of thegraphite-containing refractory.

The following describes the effects of the amounts of alumina rawmaterial, silicon carbide raw material, and silica raw material for usein a refractory liner for a molten iron preliminary treatment vessel onthe bending strength, breaking strength, erosion resistance, and crackresistance of a graphite-containing refractory. Table 12 shows theproduction conditions and evaluation results of testedgraphite-containing refractories.

TABLE 12 Example Example Example Example Example Example Particle size(mm) Unit 11-1 11-2 11-3 11-4 11-5 11-6 Refractory Al₂O₃ 3-5 mass % 1.52.3 3.3 5.0 5.0 4.2 raw 1 or more and 3.0 4.7 6.7 10.0 10.0 8.3 materialless than 3 0.3 or more and 3.0 4.7 6.7 10.0 10.0 8.3 less than 1 50-200Mesh 1.5 2.3 3.3 5.0 5.0 4.2 (0.075 or more and less than 0.3) SiO₂ 1 ormore and 0.3 0.3 0.5 5.0 25.0 27.5 less than 3 0.3 or more and 0.3 0.30.5 5.0 25.0 27.5 less than 1 SiC 0.5 0.5 1.0 1.0 1.0 1.0 Flake — 90.085.0 78.0 59.0 19.0 19.0 graphite Metallic Si — 2.3 2.3 2.3 2.3 2.3 2.3powder Hexamine — 0.3 0.3 0.3 0.3 0.3 0.3 Phenolic — 3 3 3 3 3 3 resinTotal 105.6 105.6 105.6 105.6 105.6 105.6 Carbon Fiber Length mm 600fibers shape Diameter μm/fiber 7 Number of fiber 12000 bundled fibersPreliminary Phenolic resin Done treatment bonding Charging Initialcharging Vol % 10 method amount of refractory raw material relative tomold volume Second and later Vol % 15 charging amounts of refractory rawmaterial relative to mold volume Angle of ° 90 placement of carbon fiberbundle (θ2) Intervals between mm 5 carbon fiber bundles Repetition ofYes charging of raw material and placement of carbon fiber bundlesTiming of placing fiber After kneading raw materials bundles Bendingstrength MPa 10.7 14.5 18.2 18.9 19.2 19.3 Fracture energy kJ/m² 12 2022 21 23 24 Erosion resistance — 120 120 97 101 107 110 Crack resistanceE₃/E₀ 0.46 0.50 0.55 0.53 0.63 0.64 Example Example Example ExampleExample 11-7 11-8 11-9 11-10 11-11 Refractory Al₂O₃ 3-5 mass % 8.3 8.312.5 15.8 16.5 raw 1 or more and 16.7 16.7 25.0 31.7 33.0 material lessthan 3 0.3 or more and 16.7 16.7 25.0 31.7 33.0 less than 1 50-200 Mesh8.3 8.3 12.5 15.8 16.5 (0.075 or more and less than 0.3) SiO₂ 1 or moreand 5.0 15.0 2.5 1.5 0.0 less than 3 0.3 or more and 5.0 15.0 2.5 1.50.0 less than 1 SiC 1.0 1.0 1.0 1.0 0.5 Flake — 39.0 19.0 19.0 1.0 0.5graphite Metallic Si — 2.3 2.3 2.3 2.3 2.3 powder Hexamine — 0.3 0.3 0.30.3 0.3 Phenolic — 3 3 3 3 3 resin Total 105.6 105.6 105.6 105.6 105.6Carbon Fiber Length mm 600 fibers shape Diameter μm/fiber 7 Number offiber 12000 bundled fibers Preliminary Phenolic resin Done treatmentbonding Charging Initial charging Vol % 10 method amount of refractoryraw material relative to mold volume Second and later Vol % 15 chargingamounts of refractory raw material relative to mold volume Angle of ° 90placement of carbon fiber bundle (θ2) Intervals between mm 5 carbonfiber bundles Repetition of Yes charging of raw material and placementof carbon fiber bundles Timing of placing fiber After kneading rawmaterials bundles Bending strength MPa 18.8 19.0 18.1 18.3 11.4 Fractureenergy kJ/m² 21 22 20 20 14 Erosion resistance — 100 103 99 98 108 Crackresistance E₃/E₀ 0.54 0.57 0.52 0.51 0.45

As shown in Table 12, the graphite-containing refractories according toExamples 11-1 to 11-11 are graphite-containing refractories in whichcarbon fiber bundles each composed of 12000 carbon fibers 600 mm inlength and 7 μm/fiber in diameter are placed, wherein the amounts ofalumina raw material, silicon carbide raw material, silica raw material,and graphite in a graphite-containing refractory raw material arechanged. The size of each graphite-containing refractory is the same asthat in Example 2-1, and the production method is the same as the methoddescribed in Table 3. The bending strength, fracture energy, erosionresistance, and crack resistance of the graphite-containing refractoriesaccording to Examples 11-1 to 11-11 were determined.

As shown in Table 12, the graphite-containing refractories according toExamples 11-3 to 11-5 and Examples 11-7 to 11-10, in which the aluminaraw material constituted 10% to 95% by mass, the silica raw materialconstituted 1% to 50% by mass, and the silicon carbide raw materialconstituted 1% or more by mass, had high fracture energy and had bothhigh crack resistance and high erosion resistance. By contrast, thegraphite-containing refractory according to Example 11-1, in which thealumina raw material constituted 9.0% by mass and the silica rawmaterial constituted 0.6% by mass, had decreased bending strength anderosion resistance. The graphite-containing refractory according toExample 11-2, in which the silica raw material constituted 0.6% by mass,had decreased erosion resistance. The graphite-containing refractoryaccording to Example 11-6, in which the silica raw material constituted55.0% by mass, also had decreased erosion resistance. Furthermore, thegraphite-containing refractory according to Example 11-11, in which thealumina raw material constituted 99.0% by mass, had decreased bendingstrength and fracture energy. These results show that when an aluminaraw material, a silicon carbide raw material, a silica raw material, andgraphite are used in the graphite-containing refractory raw material,the alumina raw material preferably constitutes 10% to 95% by mass, thesilicon carbide raw material preferably constitutes 1% or more by mass,and the silica raw material preferably constitutes 1% to 50% by mass toincrease the bending strength and fracture energy of thegraphite-containing refractory.

The following describes the effects of the amount of refractory wasteproduced by crushing used alumina-silicon carbide-carbon refractorywaste for use in a refractory liner for a molten iron preliminarytreatment vessel on the bending strength, breaking strength, erosionresistance, and crack resistance of a graphite-containing refractory.Table 13 shows the production conditions and evaluation results oftested graphite-containing refractories.

TABLE 13 Example Example Example Example Particle size (mm) Unit 12-112-2 12-3 12-4 Refractory Refractory 3-5 mass % 5 25 45.0 47.5 raw wasteraw 1 or more and less than 3 5 25 45.0 47.5 material material Al₂O₃ 3-518.0 9.4 2.0 0.0 1 or more and less than 3 18.0 9.4 2.0 0.0 0.3 or moreand less than 1 6.0 3.1 0.0 0.0 SiO₂ 1 or more and less than 3 20.0 10.01.0 0.0 0.3 or more and less than 1 20.0 10.0 1.0 0.0 SiC 4.5 4.5 3.04.5 Flake graphite — 3.5 3.5 1.0 0.5 Metallic Si — 2.3 2.3 2.3 2.3powder Hexamine — 0.3 0.3 0.3 0.3 Phenolic resin — 3 3 3 3 Total 105.6105.6 105.6 10.6 Carbon Fiber shape Length mm 600 90 fibers Diameterμm/fiber 7 0.8 Number of bundled fibers fiber 12,000 990 PreliminaryPhenolic resin bonding Done treatment Charging Initial charging amountof refractory raw Vol % 10 method material relative to mold volumeSecond and later charging amounts of refractory Vol % 15 raw materialrelative to mold volume Angle of placement of carbon fiber bundle (θ2) °90 Intervals between carbon fiber bundles mm 5 Repetition of charging ofraw material and Yes placement of carbon fiber bundles Timing of placingfiber bundles After kneading raw materials Bending strength MPa 18.017.6 17.2 6.7 Fracture energy kJ/m² 22 21 20 0.7 Erosion resistance —108 114 120 139 Crack resistance E₃/E₀ 0.62 0.58 0.54 0.39

As shown in Table 13, the graphite-containing refractories according toExamples 12-1 to 12-4 are graphite-containing refractories in whichcarbon fiber bundles each composed of 12000 carbon fibers 600 mm inlength and 7 μm/fiber in diameter are placed, wherein the amounts ofrefractory waste, alumina raw material, silicon carbide raw material,silica raw material, and graphite in a graphite-containing refractoryraw material are changed. The size of each graphite-containingrefractory is the same as that in Example 2-1, and the production methodis the same as the method described in Table 3. The bending strength,fracture energy, erosion resistance, and crack resistance of thegraphite-containing refractories according to Examples 12-1 to 12-4 weredetermined.

Table 13 shows that the graphite-containing refractories according toExamples 12-1 to 12-3, in which the refractory waste constituted 10% to90% by mass, had almost the same crack resistance and erosion resistanceas graphite-containing refractories produced from virgin raw materialsalone. By contrast, the graphite-containing refractory according toExample 12-4, in which the refractory waste constituted 95.0% by mass,had decreased erosion resistance. These results show that whenrefractory waste produced by crushing used alumina-siliconcarbide-carbon refractory waste is used in the graphite-containingrefractory raw material, the refractory waste preferably constitutes 10%to 90% by mass to increase the bending strength and fracture energy ofthe graphite-containing refractory.

The following describes the effects of the amounts of alumina rawmaterial and silicon carbide raw material in an alumina carbongraphite-containing refractory on the bending strength, breakingstrength, erosion resistance, and crack resistance of agraphite-containing refractory. Table 14 shows the production conditionsand evaluation results of tested graphite-containing refractories.

TABLE 14 Example Example Example Example Example Example Particle size(mm) Unit 13-1 13-2 13-3 13-4 13-5 13-6 Refractory Al₂O₃ 3-5 mass % 1.03.2 6.7 10.0 13.3 16.3 raw 1 or more and less than 3 2.0 6.3 13.3 20.026.7 32.7 material 0.3 or more and less than 1 2.0 6.3 13.3 20.0 26.732.7 50-200 Mesh 1.0 3.2 6.7 10.0 13.3 16.3 (0.075 or more and less than0.3) SiC 1.0 1.0 1.0 1.0 1.0 1.0 Flake graphite — 93.0 80.0 59.0 39.019.0 1.0 Metallic Si — 2.3 2.3 2.3 2.3 2.3 2.3 powder Hexamine — 0.3 0.30.3 0.3 0.3 0.3 Phenolic resin — 3 3 3 3 3 3 Total 105.6 105.6 105.6105.6 105.6 105.6 Carbon Fiber shape Length mm 600 fibers Diameterμm/fiber 7 Number of bundled fibers fiber 12000 Preliminary Phenolicresin bonding Done treatment Charging Initial charging amount ofrefractory raw Vol % 10 method material relative to mold volume Secondand later charging amounts of Vol % 15 refractory raw material relativeto mold volume Angle of placement of carbon fiber bundle ° 90 (θ2)Intervals between carbon fiber bundles mm 5 Repetition of charging ofraw material and Yes placement of carbon fiber bundles Timing of placingfiber bundles After kneading raw materials Bending strength MPa 10.714.0 17.9 18.0 18.0 11.0 Fracture energy kJ/m² 12 20 21 22 22 13 Erosionresistance — 120 114 101 100 102 101 Crack resistance E₃/E₀ 0.46 0.500.53 0.54 0.52 0.45

As shown in Table 14, the graphite-containing refractories according toExamples 13-1 to 13-6 are graphite-containing refractories in whichcarbon fiber bundles each composed of 12000 carbon fibers 600 mm inlength and 7 μm/fiber in diameter are placed, wherein the amounts ofalumina raw material, silicon carbide raw material, and graphite in agraphite-containing refractory raw material are changed. The size ofeach graphite-containing refractory is the same as that in Example 2-1,and the production method is the same as the method described in Table3. The bending strength, fracture energy, erosion resistance, and crackresistance of the graphite-containing refractories according to Examples13-1 to 13-6 were determined.

Table 14 shows that the graphite-containing refractories according toExamples 13-2 to 13-5, in which the alumina raw material constituted 10%to 95% by mass, maintained high bending strength and fracture energy andhad both high crack resistance and high erosion resistance. By contrast,the graphite-containing refractory according to Example 13-1, in whichthe alumina raw material constituted 6.0% by mass, had decreased bendingstrength and fracture energy. The graphite-containing refractoryaccording to Example 13-6, in which the alumina raw material constituted98% by mass, could not prevent cracking caused by thermal spalling andhad decreased crack resistance and erosion resistance. These resultsshow that when an alumina-carbon system graphite-containing refractoryis used, the alumina raw material preferably constitutes 10% to 95% bymass, and the silicon carbide raw material preferably constitutes 1% ormore by mass to increase the bending strength and fracture energy of thegraphite-containing refractory.

The following describes the effects of the amounts of silica rawmaterial and silicon carbide raw material in a silicacarbon systemgraphite-containing refractory on the bending strength, breakingstrength, erosion resistance, and crack resistance of agraphite-containing refractory. Table 15 shows the production conditionsand evaluation results of tested graphite-containing refractories.

TABLE 15 Comparative Example Example Example Example Particle size (mm)Unit example 14-1 14-1 14-2 14-3 14-4 Refractory SiO₂ 1 or more and lessthan 3 mass % 0.0 9.5 17.0 25.0 49.0 raw 0.3 or more and less than 1 0.09.5 17.0 25.0 49.0 material SiC 1.0 1.0 1.0 1.0 1.0 Flake graphite —99.0 80.0 65.0 49.0 1.0 Metallic Si — 2.3 2.3 2.3 2.3 2.3 powderHexamine — 0.3 0.3 0.3 0.3 0.3 Phenolic resin — 3 3 3 3 3 Total 105.6105.6 105.6 105.6 105.6 Carbon Fiber shape Length mm 600 fibers Diameterμm/fiber 7 Number of bundled fibers fiber 12000 Preliminary Phenolicresin bonding Done treatment Charging Initial charging amount of Vol %10 method refractory raw material relative to mold volume Second andlater charging Vol % 15 amounts of refractory raw material relative tomold volume Angle of placement of carbon ° 90 fiber bundle (θ2)Intervals between carbon mm 5 fiber bundles Repetition of charging ofYes raw material and placement of carbon fiber bundles Timing of placingfiber bundles After kneading raw materials Bending strength MPa 6.6 17.718.0 17.8 11.1 Fracture energy kJ/m² 1 21 22 22 13 Erosion resistance —140 101 100 102 119 Crack resistance E₃/E₀ 0.40 0.50 0.51 0.50 0.45

As shown in Table 15, the graphite-containing refractories according toExamples 14-1 to 14-4 and Comparative Example 14-1 aregraphite-containing refractories in which carbon fiber bundles eachcomposed of 12000 carbon fibers 600 mm in length and 7 μm/fiber indiameter are placed, wherein the amounts of silica raw material, siliconcarbide raw material, and graphite in a graphite-containing refractoryraw material are changed. The size of each graphite-containingrefractory is the same as that in Example 2-1, and the production methodis the same as the method described in Table 3. The bending strength,fracture energy, erosion resistance, and crack resistance of thegraphite-containing refractories according to Examples 14-1 to 14-4 andComparative Example 14-1 were determined.

Table 15 shows that the graphite-containing refractories according toExamples 14-2 and 14-3, in which the silica raw material constituted 1%to 50% by mass, maintained high bending strength and fracture energy andhad both high crack resistance and high erosion resistance. By contrast,the graphite-containing refractory according to Example 14-1, in whichthe silica raw material constituted less than 1% by mass, hadsignificantly decreased erosion resistance due to the small amount ofsilica raw material and the large amount of graphite as large as 99.0%by mass. The graphite-containing refractory according to Example 14-4,in which the silica raw material constituted 98.0% by mass, could notprevent cracking caused by thermal spalling and had decreased crackresistance and fracture energy. These results show that when asilica-carbon system graphite-containing refractory is used, the silicaraw material preferably constitutes 1% to 50% by mass to increase thebending strength and fracture energy of the graphite-containingrefractory.

The following describes the effects of short carbon fibers on thebending strength, breaking strength, erosion resistance, and crackresistance of a graphite-containing refractory containing the shortcarbon fibers. Table 16 shows the production conditions and evaluationresults of tested graphite-containing refractories.

TABLE 16 Example Example Example Example Example Example Example ExampleExample Particle size (mm) Unit 15-1 15-2 15-3 15-4 15-5 15-6 15-7 15-815-9 Refractory MgO 3-5 mass % 10 raw 1 or more and less 30 materialthan 3 0.3 or more and 30 less than 1 50-200 mesh 15 (0.075 or more andless than 0.3) Flake — 15 graphite Metallic Si — 2.3 powder Hexamine —0.3 Phenolic — 3 resin Short Fiber diameter μm/fiber 1 1 1 25 50 1 1 1 1carbon Fiber length μm 2 2 2 1000 100 2000 1 2 2 fibers (1 mm) (2 mm)Fiber length/fiber — 2 2 2 40 2 2000 1 2 2 diameter Amount mass % 0.10 110 1 1 1 1 0.05 15 Total mass % 105.7 106.6 115.6 106.6 106.6 106.6106.6 105.7 120.6 Carbon Fiber Length mm 600 fiber bundle Diameterμm/fiber 7 bundle shape Number of Fiber 12000 bundled fibers PreliminaryPhenolic resin Done treatment bonding Charging Initial charging Vol % 10method amount of refractory raw material relative to mold volume Secondand later Vol % 15 charging amounts of refractory raw material relativeto mold volume Angle of ° 90 placement of carbon fiber bundle (θ2)Intervals between mm 5 carbon fiber bundles Repetition of Yes chargingof raw material and placement of carbon fiber bundles Timing of placingfiber bundles After kneading raw materials Bending strength MPa 28.929.6 29.0 29.2 23.9 24.2 23.5 23.8 23.8 Fracture energy kJ/m² 56 58 5556 47 47 45 46 46 Erosion resistance — 101 100 100 100 102 102 101 102102 Crack resistance E₃/E₀ 0.71 0.74 0.72 0.72 0.67 0.69 0.67 0.68 0.68

As shown in Table 16, the graphite-containing refractories according toExamples 15-1 to 15-9 are graphite-containing refractories in whichcarbon fiber bundles each composed of 12000 carbon fibers 600 mm inlength and 7 μm/fiber in diameter are placed, whereingraphite-containing refractory raw materials containing differentamounts of short carbon fibers with different fiber diameters and fiberlengths are used. The size of each graphite-containing refractory is thesame as that in Example 2-1, and the production method is the same asthe method described in Table 3. The bending strength, fracture energy,erosion resistance, and crack resistance of the graphite-containingrefractories according to Examples 15-1 to 15-9 were determined.

As shown in Table 16, the graphite-containing refractories according toExamples 15-1 to 15-4, in which short carbon fibers with a fiberdiameter of 1 to 25 μm/fiber, a fiber length of 2 to 1000 μm, and aratio of fiber length to fiber diameter of 2 to 40 constituted 0.10% to10% by mass based on 100% by mass of the graphite-containing refractoryraw material, had high bending strength and fracture energy. Thegraphite-containing refractory according to Example 15-5 containingshort carbon fibers with a fiber diameter of more than 45 μm/fiber, morespecifically 50 μm/fiber, underwent lamination during pressing due tothe large fiber diameter of the short carbon fibers. Thus, thegraphite-containing refractory according to Example 15-5 had lowerbending strength and fracture energy than the graphite-containingrefractories according to Examples 15-1 to 15-4.

The graphite-containing refractory according to Example 15-6 containingshort carbon fibers with a fiber length of more than 1000 μm (1 mm),more specifically 2000 μm (2 mm), underwent lamination during pressingdue to poor entanglements between the carbon fibers and the refractoryraw material. Thus, the graphite-containing refractory according toExample 15-6 had lower bending strength and fracture energy than thegraphite-containing refractories according to Examples 15-1 to 15-4.

The graphite-containing refractory according to Example 15-7 containingshort carbon fibers with a ratio of fiber length to fiber diameter ofless than 2, more specifically 1, had lower bending strength andfracture energy than the graphite-containing refractories according toExamples 15-1 to 15-4 due to poor entanglements between the carbonfibers and the refractory raw material.

The graphite-containing refractory according to Example 15-8, in whichshort carbon fibers constituted less than 0.10% by mass, morespecifically 0.05% by mass, had no suppressive effect of the shortcarbon fibers on the development of a crack in the refractory due to theexcessively small amount of carbon fibers. Thus, the graphite-containingrefractory according to Example 15-8 had lower bending strength andfracture energy than the graphite-containing refractories according toExamples 15-1 to 15-4.

The graphite-containing refractory according to Example 15-9, in whichshort carbon fibers constituted more than 10% by mass, more specifically15% by mass, underwent lamination during pressing due to no entanglementbetween the carbon fibers and the refractory raw material. Thus, thegraphite-containing refractory according to Example 15-9 had lowerbending strength and fracture energy than the graphite-containingrefractories according to Examples 15-1 to 15-4.

These results show that short carbon fibers with a fiber diameter of 1to 25 μm/fiber, a fiber length of 2 to 1000 μm, and a ratio of fiberlength to fiber diameter of 2 to 40 preferably constitute 0.10% to 10%by mass based on 100% by mass of a graphite-containing refractory rawmaterial to increase the bending strength and fracture energy of agraphite-containing refractory.

1.-21. (canceled)
 22. A graphite-containing refractory with a graphitecontent of 1% to 80% by mass, comprising: a carbon fiber bundle 100 mmor more in length placed therein, the carbon fiber bundle being formedof 1000 to 300000 carbon fibers with a fiber diameter of 1 to 45μm/fiber.
 23. The graphite-containing refractory according to claim 22,wherein the carbon fiber bundle is formed of 1000 to 60000 carbonfibers.
 24. The graphite-containing refractory according to claim 22,comprising a magnesia raw material constituting 20% to 99% by mass ofthe graphite-containing refractory.
 25. The graphite-containingrefractory according to claim 22, comprising an alumina raw materialconstituting 10% to 95% by mass of the graphite-containing refractoryand a silicon carbide raw material constituting 1% or more by mass ofthe graphite-containing refractory.
 26. The graphite-containingrefractory according to claim 25, further comprising a silica rawmaterial constituting 1% to 50% by mass of the graphite-containingrefractory.
 27. The graphite-containing refractory according to claim22, comprising a refractory waste constituting 10% to 90% by mass of thegraphite-containing refractory, the refractory waste being a crushedused refractory.
 28. The graphite-containing refractory according toclaim 22, wherein the carbon fiber bundle is formed by bonding using atleast one adhesive selected from the group consisting of a phenolicresin, an epoxy resin, a melamine resin, a urea resin, an alkyd resin,an unsaturated polyester resin, polyurethane, thermosetting polyimide,an alumina sol, a silica sol, a zirconia sol, a chromia sol, a titaniasol, a magnesia sol, a calcia sol, an yttria sol, pitch, tar, and astarch paste.
 29. The graphite-containing refractory according to claim22, further comprising short carbon fibers constituting 0.10% to 10% bymass based on 100% by mass of the graphite-containing refractory, theshort carbon fibers having a fiber diameter of 1 to 45 vim/fiber, afiber length of 1 mm or less, and a ratio of fiber length to fiberdiameter (fiber length/fiber diameter) of 2 to
 1000. 30. A method ofproducing a graphite-containing refractory within which a carbon fiberbundle is placed, the graphite constituting 1% to 80% by mass, themethod comprising: a bundling step of bundling carbon fibers to form thecarbon fiber bundle; a mixing step of mixing a refractory raw materialwith graphite to prepare a graphite-containing refractory raw material;a pressing step of pressing the graphite-containing refractory rawmaterial in which the carbon fiber bundle is placed to prepare a formedproduct; and a drying step of drying the pressed product, wherein thebundling step includes bundling 1000 to 300000 of the carbon fibers witha fiber diameter of 1 to 45 μm/fiber to form a carbon fiber bundle 100mm or more in length.
 31. The method according to claim 30, wherein thebundling step includes bundling 1000 to 60000 of the carbon fibers. 32.The method according to claim 30, wherein the refractory raw material isa magnesia raw material, and the mixing step includes adding 20% to 99%by mass of the magnesia raw material.
 33. The method according to claim30, wherein the refractory raw material includes an alumina raw materialand a silicon carbide raw material, and the mixing step includes adding10% to 95% by mass of the alumina raw material and adding the siliconcarbide raw material at 1% or more by mass.
 34. The method according toclaim 33, wherein the refractory raw material includes an alumina rawmaterial, a silicon carbide raw material, and a silica raw material, themixing step includes adding 10% to 95% by mass of the alumina rawmaterial, adding the silicon carbide raw material at 1% or more by mass,and adding 1% to 50% by mass of the silica raw material.
 35. The methodaccording to claim 30, wherein the refractory raw material is arefractory waste, which is a crushed used refractory, and the mixingstep includes adding 10% to 90% by mass of the refractory waste.
 36. Themethod according to claim 30, wherein the bundling step includes bondingthe carbon fibers with at least one adhesive selected from the groupconsisting of a phenolic resin, an epoxy resin, a melamine resin, a urearesin, an alkyd resin, an unsaturated polyester resin, polyurethane,thermosetting polyimide, an alumina sol, a silica sol, a zirconia sol, achromia sol, a titania sol, a magnesia sol, a calcia sol, an yttria sol,pitch, tar, and a starch paste.
 37. The method according to claim 30,further comprising, before the pressing step: a kneading step ofkneading the graphite-containing refractory raw material; and a fillingstep of filling a mold to press the graphite-containing refractory rawmaterial with the kneaded graphite-containing refractory raw materialand the carbon fiber bundle.
 38. The method according to claim 37,wherein the filling step includes filling 5% or more by volume of themold with the graphite-containing refractory raw material, then placingthe carbon fiber bundle at intervals of 3 mm or more, and repeatedlyperforming the filling and the placing to fill the mold with thegraphite-containing refractory raw material and the carbon fiber bundle.39. The method according to claim 30, further comprising, before thepressing step: a kneading step of kneading the graphite-containingrefractory raw material; and a filling step of filling a pressing vesselto press the graphite-containing refractory raw material with thekneaded graphite-containing refractory raw material and the carbon fiberbundle, wherein the pressing step includes applying pressure to thepressing vessel via a pressure medium to prepare a pressed product. 40.The method according to claim 30, wherein the mixing step includesadding short carbon fibers constituting 0.10% to 10% by mass based on100% by mass of the graphite-containing refractory raw material, theshort carbon fibers having a fiber diameter of 1 to 45 μm/fiber, a fiberlength of 1 mm or less, and a ratio of fiber length to fiber diameter(fiber length/fiber diameter) of 2 to 1000.